214 
ON DISEASES OF THE DENTAL APPARATUS 
2. Anomalies in the form of the arcades and in the direction 
of the teeth . — We have said in our preliminary considerations, that 
the dental arcades formed at the superior maxilla two curves op- 
posed by their concavities, and, at the inferior maxilla, two lines 
nearly straight, converging the oue to the other towards the sym- 
physis of the chin. These directions may, owing in some cases to 
congenital conformation, be very irregular. We observe some- 
times, in fact, that the curves of the upper jaw are effaced ; at 
other times, and most frequently, that the lines of the lower jaw 
are incurvated within the arcade. Either of these deformities may 
exist isolated or simultaneously. 
It therefore results from this, that, in the approach of the jaws, 
the relation is not identically established between the surfaces of 
friction ; and the consequence of this disposition is, an irregularity 
in the wear, which permits the abnormal development of the 
border of the tables, within at the lower jaw, and without at the 
superior ; and hence a hinderance in mastication. 
3. Exuberance of some particular parts of the dental appa- 
ratus . — The deformities of which we are now about to speak are 
those most frequently encountered : — 
A. The superior molars are, as we have said in commencing, 
larger and longer than those of the inferior maxilla, so that, in 
order that the friction may be established in the entire breadth of 
the superior tabular surfaces, it is necessary that there should exist 
a forced lateral movement of the inferior jaw upon the superior. 
In some animals, perhaps because the movement is not effected 
throughout the extreme limits of the segment of the circle that 
may be described during mastication by the jaw, the external 
border of the dental tables does not wear sufficiently, and therefore 
becomes elevated and sharp. 
Each of the free extremities of the salient columns which sepa- 
rate the fluted cannulse at the external side of the teeth, become 
then so many sharp points, which tear the buccal membrane within 
the cheeks, and determine very acute pain. 
At other times, it is at the internal border of the molars of the 
inferior jaw that this effect manifests itself. Then it is the tongue 
that is painfully excoriated by the angular asperities presented by 
the cutting border of the teeth. 
In some rare cases, when the cause, difficult to determine, 
which produces this deformity continues in action, the dental tables, 
which present a normal inclination inverse in the two jaws, at 
length form planes very oblique. This obliquity is sometimes so 
great that, at the under jaw, the internal borders of the teeth are 
very elevated, while the external is almost on a level with the 
gums. The inverse effect manifests itself at the upper jaw : the 
